The invention relates to a method and a device for rapidly detecting the position of a target with the aid of a theodolite having a spatially resolving opto-electronic detector having pixels arranged in the form of a matrix, it being the case that
a) the target emits or reflects radiation, PA1 b) the radiation coming from the target is received by the imaging optical system and the detector of the theodolite, and PA1 c) the detector signals are evaluated.
Such methods and devices are known from the journal "Technische Rundschau" No. 39,1988, pages 14-18, "Theodolitsysteme fur industrielle und geodatische Messungen", ("Theodolite systems for industrial and geodetic measurements"), W. Huep, O. Katowski and in the journal "Opticus" No. 1/94, pages 8-9 of the company Leica AG, "Theodolite-Sensoren furdie industrielle Vermessung" ("Theodolite sensors for industrial surveying").
These publications describe the use of such methods and devices in geodetic surveying, in building surveying and in industrial measurement technology. The general aim is to determine the three-dimensional coordinates of points in space. Targets, for example surface-reflecting spheres, reflecting foils or radiation-emitting targets are positioned at these points and sighted using a theodolite telescope. Triangulation or the polar method are customary in the case of three-dimensional determination of coordinates. In triangulation, two theodolites at a known spacing from one another are aimed at the targets and determine the horizontal and vertical angles with reference to their base line. The polar method employs a tachymeter which comprises a theodolite having an integrated distance meter. The three-dimensional coordinates of the target are likewise calculated from the determination of angle and distance.
In addition to determining and recording coordinates, it is also possible conversely to lay off coordinates on site which are recorded in a plan or can be taken from a map. For example, in road building the route is laid off by means of theodolites or a tachymeter and a rod provided with a target. As operators, this requires at least two people who communicate by hand signals or by radio. On the one hand, the coordinates prescribed according to the plan are set at the surveying instrument, while, on the other hand, the rod with the target is moved until the target has reached the desired coordinates.
It is possible to regard as quasi-continuous laying off applications in which road-driving machines are to keep to a specific path in road building or else in tunneling or mining. These machines, to which a target is attached, are controlled with the aid of a theodolite. In this case, deviations from the desired direction when the machines are being driven forward are detected on the basis of deviating horizontal or vertical angles.
In modern surveying instruments, the visual observation of the target via the theodolite telescope is supported by electronic detection of the target. Use is made of video cameras or of spatially resolving opto-electronic detectors such as, for example, two-dimensional CCD arrays, which are integrated in the imaging optical system of the theodolite. In addition to the literature quoted above, such a system is also described in DE 34 24 806 C2. Image processing is used firstly to determine the coordinates of the target image in the coordinate system of the spatially resolving detector. These are employed to calculate on the basis of a calibration the layer angles of angles from which, in turn, the three-dimensional coordinates of the target in space are calculated in the normal way by means of triangulation or the polar method.
Substantial time is expended on processing because of the large data volumes of image information and is a disadvantage in image processing. Each pixel of a CCD array supplies an intensity value which is transmitted into a computer, usually a PC. Since the number of pixels is of the order of magnitude of 1 million in many CCD arrays, it is a problem if the CCD array is to be read out very often per second and thus many images are to be transmitted per second into the computer for evaluation and to be evaluated at the same time. However, this is precisely what is required for automatic detection of a target or for tracking it automatically. Such image processing for aims of this sort cannot be done in time even using the fast microprocessors currently available.
It is therefore the object of the invention to specify a method and a device so as automatically to detect a target in a short time with little outlay, to determine its coordinates, to track its movement and to record the path data.
The object is achieved by virtue of the fact that the detector signals are fed to a preprocessing unit and that in the preprocessing unit the radiation intensities detected by the pixels of the detector are summed by row and column, in that a row sum function is formed from the sums of the rows and a column sum function is formed from the sums of the columns, and in that the two-dimensional image coordinates of the target in the coordinate system of the detector are determined from the determination of the centroid of the row sum function and column sum function. Furthermore, the object is achieved by the Device described herein. Advantageous embodiments of the invention are also described.
Cooperative targets are used for the invention. Cooperative targets are either fitted with radiating sources which emit light, preferably in the infrared or visible wavelength region, or use is made of reflecting targets which are illuminated by a radiating source. This can be integrated in the theodolite and likewise emit in the infrared or visible wavelength region.
FIG. 4 shows a flowchart of a method for detecting the position of a cooperative target and is described in detail below.
The light emitted or reflected by the target is received by the imaging optical system of the theodolite and projected onto a spatially sensitive optoelectronic detector (step 101). The imaging consists of a light patch having a specific intensity distribution. The latter is detected in a spatially resolved fashion by the light-sensitive structures of the detector. In CCD arrays, the light-sensitive structures are arranged as pixels in the form of a matrix, that is to say in the fashion of rows and columns. The electric signals read out from the detector (step 102) correspond to the intensity distribution of the light patch. The electric signals are read into a pre-processing unit connected to the detector.
According to the invention, the pixel image of the target is separated into two sum functions by means of an appropriately designed hardware in the pre-processing unit. The intensity values of all the pixels of a row are firstly added up for this purpose (step 104). They form a sum value belonging to this row. The sum values of all the rows produce a row sum function as a function of the row number (step 106). Using known mathematical methods, the centroid of the row sum function is determined, and thus supplies a coordinate value in the coordinate system of the detector. The intensity values of the pixels of each column are added up in a similar way (step 104). The centroid, and thus the second coordinate in the coordinate system of the detector are likewise calculated from the column sum function thus produced (step 108). As a result, the two-dimensional image coordinates of the target are determined on the detector (step 110).
The two-dimensional image coordinates of the target are converted into a horizontal and a vertical angle on the basis of calibration values. The angles relate to a sighting axis which, for example, can be the optical axis of the imaging optical system of the theodolite. The sighting axis itself is given in a defined global coordinate system.
The evaluation according to the invention of the target image signifies a drastic reduction in data. Instead of many pixel values, only the sum functions or, if appropriate, only the coordinates of the target image remain to be transmitted into an external arithmetic unit such as, for example a PC. Lengthy evaluation of all the pixels in the PC is eliminated. Of course, the data can also be further processed in an internal arithmetic unit, which is directly coupled to the preprocessing unit.
The substantial gain in time in detecting a target can, on the one hand, be used to the effect that the target need be sighted only coarsely. The target is detected automatically and its coordinates or angular coordinates are determined automatically. They can, for example, be represented on a display. The data can be further processed or stored by the arithmetic unit. The coarse sighting of the target is possible via the theodolite's telescope or via a peep-sight. In the simplest case, it is even sufficient to sight the target via a rear sight notch and front sight, which can be provided as markings on the theodolite. The telescope eyepiece can thereby be eliminated.
A search run can be started if, during coarse sighting, the target is not immediately located in the detection range of the imaging optical system. This presupposes that the vertical and tilt axes of the theodolite are motorized. The theodolite is moved about these axes by means of a search algorithm, until the target is acquired by the imaging optical system and detected by the detector. The search operation and the subsequent coordinate measurement are carried out completely automatically.
It has emerged from a large number of tests that the spatial resolution in the determination of the coordinates of the target in accordance with the invention is surprisingly good and satisfies the requirements in most applications. If, nevertheless, a higher measuring accuracy is required, this can be achieved by longer integration times, that is to say exposure times of the detector, by averaging over a plurality of images, or by refined calibration or image analysis for the purpose of reducing errors. The increased measuring accuracy makes demands on the measuring time. It is therefore provided that the detector is optionally read out synchronously with the video clock or with a frequency matched to the respective application.
It has emerged, furthermore, that it is also possible for undesired stray reflections to be detected and eliminated from the characteristic of the row and column sum functions. Stray reflections come about owing to reflections of the target radiation or illumination radiation on surfaces such as, for example, on water surfaces. Reflections falling into the imaging optical system at different angles lead to changes in the characteristic of the sum functions, which can therefore be detected and corrected.
Likewise, blooming of the detector can be determined from the characteristic of the sum functions. Better suited exposure parameters can be calculated therefrom and automatically set.
It has also emerged that a target imaged unsharply on the detector can be detected just as reliably and precisely as a sharply imaged target. Thus, a cost effective imaging optical system with a suitable permanently set focus is sufficient.
In addition to the automatic detection of a target, the invention also makes it possible to track the target automatically when the latter is, for example, moved from one lay off point or measuring point to the next. In this case, operating the entire system requires only one person, who carries the target to the points to be laid off or measured and positions it there. The theodolite automatically tracks the moving target. For this purpose, the detector of the theodolite detects the target image continuously. The read-out frequency of the detector is set accordingly. The detector signals are evaluated at least just as quickly in the preprocessing unit, and the coordinates of the target image are determined. In the case of varying coordinates of the target image on the detector, it is possible given the presence of vertical-axis and tilt-axis motors of the theodolite for these to be driven in such a way that the theodolite automatically tracks the target. The target image thereby always remains on the light-sensitive active surface of the detector.
If obstacles occur during tracking of the target which interrupt the optical contact of the theodolite with the target, a suitable search algorithm can be used to redetect the target when it reemerges beyond the obstacles. Clearly, the quick detection and determination of coordinates of targets according to the invention is indispensable for the described tracking of targets.
If, in addition, a distance meter, which can be integrated in the theodolite, is used to measure the distances to a moving target, the path of the target is described from the continuous detection of the three-dimensional coordinates of the target. The path data can be stored electronically or recorded permanently on a storage medium.